Electrolytic recovery of zinc



Patented June 23, 1931 UNITED STATES PATENT OFFICE HARRY HEY AND ARTHUR FANNIN EVANS, OF MELBOURNE, VICTORIA, AND ROWLAND THOMAS DRYLL WILLIAMS AND ARCHIBALD PHILIP NEWALL, 0F RISDON, HOBART,

TASMANIA, AUSTRALIA, ASSIGNORS T0 ELECTROLYTIC ZINC COMPANY OF AUSTRALASIA'LIMITED, OF MELBOURNE, AUSTRALIA ELECTROLYTIC RECOVERY OF ZINC No Drawing. Application filed December 17 1927, Serial No. 240,923, and in Australia December 29, 1926.

This invention relates to certain improvements in the electrolytic recovery of zinc and refers more especially to the electrolysis of zinc sulphate solutions obtained from the leaching of roasted zinc ores with sulphuric acid or spent electrolyte.

In the electrolysis of zinc sulphate solutions as at present practised, it is customary to employ lead anodes and aluminum cathodes and it is usual to add a small amount of glue for the purposes of inhibiting the toxic effect of cobalt and/or other substances present in the solution.

In the electrolysis of zinc sulphate solutions containing say- 100 grams per litre of zinc as zinc sulphate and 100 milligrams of cobalt as cobalt sulphate, it has been found necessary to add from 3 to 4 lbs. of glue per ton of cathode zinc produced which is equivalent to from 60 to 70 milligrams of glue per litre of solution passing to the electrolytic cells. Owin to ineflicient purification small quantities o toxic elements, such as arsenic and copper, are sometimes present in the electrolyte. Owing to the presence of these toxic substances and possibly other causes the am-' pere eiiiciency o the electrolysis is sometimes reduced and the quality of the cathode zinc,

produced affected.

The object of this invention is to provide certain improvements in the electrolysis of zinc sulphate solutions whereby improved current eificien'cies may be obtained.

We have found if the electrolysis of zinc sulphate solutions is carried out in'the pres ence of small amounts .of antimony in the electrolyte, such amounts being less than will materially afl'ect the nature of the zinc deposited on the cathodes, improved current efliciencies can be obtained. By small quantities we mean 0.5 milligrams per litre or less.

Consequently this invention comprises the addition to the electrolyte of such quantities of antimony as will ensure improved current efliciencies (such as by counteracting the deleterious eflect of toxic compounds) but less than such quantities as will afiect the nature or condition of the zinc deposited on the cathodes.

The addition of antimony to" the electrolyte for the purpose of this invention may be efi'ected either in the form of a soluble salt such as antimony, tartrate, or by the use of anodes containing antimony.

Care must be exercised in seeing that an excessive amount of antimony is not present whether derived from soluble salts of antimony added direct to the electrolyte, or from antimonial lead anodes, as excessive amounts will give a Very rough deposit of cathode zinc which yields excessive dross when melted. It is therefore necessary to see that the addition of antimony to the electrolyte is closely controlled.

The quantity of antimony present may be judged by the usual well-known characteristics of the zinc plates on the cathodes and such characteristics will aiford a guide to the amount of additions of antimony which may be permitted.

Experiments have shown that with an electrolyte which upon electrolysis produced a spent solution containing from to 65 grams of sulphuric acid per litre, appreciably better ampere efficiencies have been obtained with antimony present to the extent of from 0.1 to .5 milligrams per litre as compared with the same conditions when antimony was absent.

A further advantage arises from the modification of this invention wherein the antimony is added to the electrolyte through the medium of an antimonial lead anode in that the antimony strengthens the anode and renders it less liable to buckling or warping whereby a more even current density may be obtained in the cells increasing the over-all ampere efiiciency.

In this connection we have found that anodes composed of an alloy of lead and antimony in which the antimony content is from one half A,) to one and one half (1 per cent give very satisfactory results, having regard to current efliciencies on the one hand and the condition of the cathode zinc deposited on the other.

We claim:

1. In the electrolysis of zinc sulphate solutions, containing a toxic substance of the nature of cobalt, the addition to the electrolyte of a soluble salt of antimony in such quantities as will be less than will materially affect the nature of the zinc deposited on the cathodes but sufiicient to counteract the deleterious effect of the said toxic substance.

2. In the electrolytic recovery of zinc, the electrolysis of zinc sulphate solutions, containing a toxic substance of the nature of cobalt, the addition to the electrolyte of a soluble salt of antimony in such quantities as will provide an antimony content in the electrolyte of from about 0.1 to about 0.5 milli grains of antimony per litre.

In Witness whereof We hereunto aflix our signatures.

HARRY HEY.

ARTHUR FANMN EVANS.

ROWLAND THUMAS DRYLL WILLIAMS. ARCE'HEALD PHILIP NEWALL. 

